Many pad assemblies include a multiplicity of aligned flexible sheets (i.e., typically paper sheets) in a stack which are attached together along or adjacent aligned edges of the sheets. Some such pad assemblies are large in size and include a stiff back card on which the stack is mounted so that the pad assembly can be supported at the front of a room on a support such as an easel during a meeting and used to record lists of items or ideas generated during the meeting. During such use, typically one or more of the uppermost sheets on the pad, after being written on, are either (1) bent or pivoted away from an underlying sheet so that they project over and are supported on an upper support edge of the back card and the underlying sheet can be written on, or (2) are separated from the stack so that the separated sheet or sheets can be positioned elsewhere, typically on the walls of the room to which they are attached by means such as a clip, pin or a length of adhesive coated tape so that information on the separated sheets can easily be viewed by the participants of the meeting. In some such pad assemblies, the sheets are attached together by a layer of padding compound along the one edge portion which allows the individual sheets to be separated from the padding compound or pivoted away from underlying sheets by bending the layer of padding compound. In the most common type of such pad assemblies, the sheets are attached together by staples through portions of the sheets adjacent the aligned edges of the sheets. Such staples more firmly hold the sheets together, but require portions of the sheets around the staples to be bent when the sheets are supported on the support edge and to be torn away when the sheets are removed from the pad; whereas in yet other type of such pad assemblies, the sheets are attached together by staples through portions of the sheets adjacent the aligned edges of the sheets and are transversely perforated just below the staples so that the sheets can be torn off along their lines of perforation, or folded along the lines of perforations when the sheets are supported on the support edge.
A pad assembly commercially designated "Clingers" and available from the Ampad Corporation, Holyoke, Md., comprises a multiplicity of flexible sheets disposed in a stack with the corresponding edges of the sheets aligned and with each sheet having a band of repositionable pressure sensitive adhesive coated on its rear surface along aligned first edges of the sheets, and the band of repositionable pressure sensitive adhesive on each sheet adhering it to the front surface of the adjacent sheet in the stack. Sheets removed from the "Clingers" pad assembly can be releasably adhered to a support surface by the bands of repositionable pressure sensitive adhesive on the sheets. Only the top sheet from such a pad assembly can be easily removed, however, which is a significant disadvantage of such a pad assembly compared to the pad assemblies described above from which underlying sheets in the pad can be easily removed prior to removal of the uppermost sheet in the pad. Also, the pressure sensitive adhesive on the sheets from the "Clingers" pad assembly will not very stick long to anything but the smoothest of wall surfaces, such as painted sheet rock and metal surfaces, glass, or the like.
In distinction to the above-described pad assemblies, U.S. Pat. No. 4,798,401 (Grieg) discloses a pad assembly utilizing carbonless sheets. The Grieg pad assembly comprises a multiplicity of flexible carbonless sheets disposed in a stack with the corresponding edges of the carbonless sheets aligned and with each carbonless sheet having a band of repositionable pressure sensitive adhesive coated on its rear surface along aligned first edges of the carbonless sheets, and the band of repositionable pressure sensitive adhesive on each carbonless sheet adhering it to the front surface of the adjacent sheet in the stack.
Carbonless copy papers are those which are capable of producing an image upon application of pressure. Products employing this chemistry generally contain at least two substrates (for example, two sheets of paper) and involve coating one reactant, known as a color-former, on one substrate, and the other reactant, known as a developer, on another "mating" substrate. One surface, or side, of each substrate is coated with one of the two primary reactants. The two substrates are often referred to as a donor sheet and a receptor sheet. Means for preventing the reacting of the two until intended (i.e., until activating pressure is applied) are also provided. This is typically accomplished by encapsulation of one of the reactants.
In one type of construction an encapsulated fill solution of a color-former, dissolved in appropriate hydrophobic solvent(s), is coated with a suitable binder onto a back side a sheet of paper to form the donor sheet. This donor sheet is sometimes referred to as a "coated back" (CB) sheet. Each CB coating contains rupturable capsules which, when ruptured, release reagents to produce a color-changing reaction at the adjacent CF coating. The microcapsules serve the purpose of isolating the reactants from one another and preventing reaction. A developer, also optionally in a suitable binder such as a starch or latex, is coated onto the front side of a second sheet of paper to form the receptor sheet. This receptor sheet is sometimes referred to as a "coated front" (CF) sheet. The term "suitable binder" refers to a material, such as starch or latex, that allows for dispersion of the reactants in a coating on a substrate.
Substrates, with one surface on which is coated the encapsulated color-former, and a second, opposite, surface on which is coated a developer can be placed between the CF and CB sheets, in a construction involving a plurality of substrates. Such sheets are generally referred to herein as "CFB" sheets (i.e., coated front and back sheets). Of course, each side including color-former thereon should be placed in juxtaposition with a sheet having developer thereon.
While it is customary to coat the capsules on the back surface and coat the developer on the front surface, this procedure can be reversed if desired.
In imaging, the two sheets are positioned such that the back side of the donor sheet faces the developer coating on the front side of the receptor sheet. Once activating pressure is applied to the uncoated surface of the donor sheet, such as from a stylus or business-machine key, the two substrates come into contact under sufficient pressure so that the capsules rupture (i.e., those capsules corresponding to the pattern of applied pressure) and the solution of encapsulated color-former is released and transferred from the donor sheet to the receptor sheet. On the receptor sheet, a reaction between the previously separated reactants occurs. Since the color-former and the developer form a deeply colored image when reacted, an image forms on the receptor sheet. In general, the resulting reaction will, of course, form a colored image corresponding to the path traveled by the stylus, or the pattern of pressure provided by the stylus or key and the image appearing on the receptor (CF) sheet is therefore a copy of the image applied to the top sheet. In many applications the uncoated surface of the donor (CB) sheet contains a form of some type and the activating pressure is generated by means of a pen or other writing instrument used in filling out the form. The term "activating pressure" includes, but is not limited to, pressure applied by hand with a stylus or pressure applied by a business machine key, for example, a typewriter key; and the term "encapsulation" and "encapsulated compounds" refer to microcapsules enclosing a fill material. Papers prepared in this manner and incorporating CB, CFB, and CF sheets have bee sold by 3M Company (St. Paul, Minn.) under the names of "Action 200" Carbonless Paper, and "Scotchmark" Carbonless Paper.
Another type of carbonless paper is referred to as a self-contained (SC) or autogenous carbonless paper. In self-contained carbonless papers, both the color-former, generally in encapsulated form, and developer are applied to the same side of the sheet. The color-former may be encapsulated and incorporated into the fiber lattice of the paper sheet during the manufacture of the paper. The developer, optionally in a binder, can then be coated onto the surface of the paper. Papers prepared in this manner have been sold by the 3M Company under the name of "Action 100" Carbonless Paper. Alternatively, the color-former may be encapsulated and coated with the developer, and an optional binder, onto the paper. Papers prepared in this manner have been sold by the 3M Company under the name of "Action 300" Carbonless Paper. The SC sheet is positioned below a plain-paper top sheet. In either system, when pressure is applied, again as by a typewriter or other writing instrument, the color-former capsule is ruptured and reacts with the surrounding developer to form a mark. Capsule rupture typically takes place under hand-held stylus pressure, or typical business machine key pressure.
The preparation of carbonless paper constructions employing CB, CF, and CFB sheets as well as carbonless paper constructions employing SC sheets constructions is disclosed in U.S. Pat. Nos. 3,516,846 and 3,516,941 incorporated herein by reference.
Constructions containing a first substrate surface, on which is coated the encapsulated color-former and a second substrate surface on which is coated a developer are often prepared. The coated first substrate surface is positioned within the construction in contact with the coated second substrate surface. Such a construction is known as a "set" or a "form-set" construction. Sets of 3 or more sheets can be prepared by incorporating CFB sheets between the CB and CF sheet. Thus, the sheets in the set are sequenced in the order (from top to bottom) CB, CFB(s), and CF. This insures that in each set a color former and a color developer will be brought into contact when the microcapsules containing the colorforming material are ruptured by pressure. Sets of 3 or more sheets can also be prepared by adding additional SC sheets to the construction. Carbonless paper is often used in the form of pre-printed sets, often called form-sets for preparing multiple copies of receipts, bills, and other business forms and form-sets are prepared by collating from 2 to 8 sheets.
Another carbonless paper pad assembly commercially designated "eSeetac" and available from the Barton Nelson Company of Kansas City, Mo., comprises a multiplicity of aligned flexible carbonless paper sheets. Each carbonless paper sheet is separated from the adjacent carbonless paper sheet by a divider. The carbonless paper sheets and dividers are attached along one edge portion to form a stack from which any of several uppermost individual carbonless paper sheets or dividers be pivoted away from an adjacent divider. In addition, the carbonless paper sheets can be separated from the stack and releasably adhered to a support surface by repositionable pressure sensitive on the carbonless sheet.